Discharge lamp, method of operating, and method of making



Sept- 29, 1953 G. A. FREEMAN Erm. 2,554,043

DISCHARGE LAMP, METHOD OF OPERATING, AND METHOD 0F' MAKING Filed Feb.27, -1948 *171 ZZ '29.1. 7km-Giel m i ZN\\\ a /o 2b so 4o 0 /W vd 30077M! /A/ Harmful/V06 NVENTORS G. fr. resi/14M C? 6. mwa-zsm, fr.

40 no Nm kunwr ffm/ the: ATTORNEY Patented Sept'. 29, 1953 DISCHARGELAMP,i METHOD# OPERAT- ING,.AND METHOD OF MAKING George A. Freeman, EastOrange, and Carl G. Anderson, Jr., Packanack'Lake, N. J., assignors to.Westinghousev Electric Corporatinmlttssburgh, Pag. a corporationof:Pemisylvala` Application February 27, 1948Serial No. 11,714'

7 Claims. l

This invention relatesto discharge lamps and more particularly to suchwhich may furnish instantaneous flashes of light of high intensity.

The principal object of our invention, generally considered, is toprovide a durable lamp which efficiently emits intense-flashes of lightat'Y desired time intervals.

Another object of our invention is to provide a discharge lamp, theenvelope of which has a fused quartz tubular portion unitedfat its endsto electrode-containing glass chambers which serve to collect quartzpowder vaporized during operation.

A further object of our invention is to provide a discharge lamp adaptedto emit intense flashes or light and which comprises an intermediatefused'quartz'tubular envelope portion and metal terminals holdinginwardly-extending tungsten electrodes at each end thereof, said metalter--v minals being connected to the respective ends of said tube bygraded seal portions forming-end chambers large enough to cushionthesudden expansion ofl gas in the tube during a flash.

A still further object of our invention' is to operate a lamp such asabove rdescrilavedathigher than usual power to thereby avoid blackeningand improve the operation in general.

A-n additional object of our invention is to initiate the operation of adischarge lamp, such as above described, by the employment of atriggerhaving a plurality of loops disposed around the quartz tubular portionto thereby avoid inconsistent firing.

Other objects and advantages of the invention will become apparent asthe description pro'- ceeds.

Referring to the drawing:

Figure l is an axial sectional view to scale of a lamp embodying ourinvention with parts shown in elevation, and an operating circuitindicated diagrammatically.

Figure 2 is a graph illustrating typical relations between lightintensity and duration of flash :from a lamp embodying our invention.

Figure 3 is a graph illustrating how certain of the characteristics,such as the output in lumens per watt, the peak lumens, the duration ofthe flash above one third of the peak, and the lumen seconds output,vary with the energy in each ash in terms of watt seconds, fora lampembodying our invention.

Figure 4 is a graph showing the spectrum distribution of the light froma lamp embodying our invention.

Figure 5 is a graph comparing the light output 2 and the duration oftheflash for a lamp` embodying our invention with those of a standardphotographic flash' tube, when the input of each is 48` wattlseconds-per flash.

A 'new flashing-lamp has been developed especially for safe landing ofaircraft under all weather conditions.y Instrument flying brings a planecloseto the airport where a new lighting system using lamps according toour invention provides the pilot the assurance that only direct visionIcan give f as to the runway location.

Tests conducted during the war have shown that alight can'p'enetrateVuseful distances in dense fog, providinglextremelyliigh candlepowerisused. Thelnew 'light source, ten 'times the suns brightness, hasbeen'combinedwith a large parabolic reflector to-concentrate more thanthree billion candlepower lin anarrow beamtoobtain the required fogpenetration. Thirty-six such units are installed lat ground'level,spaced in a lin-e 3200 feet long, to Aguide-apilot down to the airportrunway.

Flashing lightv was selected'as the only means of obtaining'therequired'intensity and still not blind the'pilot as'he"approached'more closely. Only a i'ewvvatt'sV average power is used by aflashing'lamp butth-ervpeak power in the flash isv millionsof watts.Extreme light intensity is produced, lasting' a fewz millionths of asecond. Suchla lamp is-operatfed-frcm energy accumulated in acondenser'whichis released at the desired A'instant by 'means'of anignition spark applied `tothe-lmnp. Before ignition, the lamp isnon-conducting. A- hi-gh voltage spark, similar to vautomobile ignition,ionizesthe gas inthe lamp causing -its'ri-'zsistance to suddenly dropfrom neaninnityto less than one ohm, dischargingthe'condenseralmos-tinstantly. The intensity of light, eventhough ofveryshortv duration, is many times greater than is `obtainable' from acontinuously lburninglamp; 'I'he'series of flashes is repeated 40 timesperv minute to keep the `pilot informed 'ofthe' location of the runwayuntil the landing*ismade` y -In determining the proper flashing lampdesign; commercial photographicfl-ash tubes were considered first. Therapidly repeating Vflash requirement wasfound toshorten lamp lifeexeessively unless"veryflowv energy per flash was used. Low flash energywas found to result in very low lamp emciency. A more rugged flashinglamp` wasrequired that also had the maximum possible light' intensity.vi

'I'heflasnlng lamp 'that was-finally developed vis lsl'iowniin-ligurelyFusedquartz is used :and

special provision made to collect vaporized quartz powder where it willnot obstruct t-he light output. The central portion of the lamp is atough vitreous tube, thick-walled to insure long life, about two incheslong and about one fifth of an inch inside diameter. A graded seal isemployed at each end to hermetically seal the low thermal expansionquartz to the higher thermal expansion metal terminals. The graded sealshave larger diameter than the quartz tube and form end cavities whichact as shock absorbers for the sudden expansion of gas during a flash.The vaporized quartz powder is blown into the end cavities where it isharmless since there it cannot absorb light output. As the lamp is used,the thick quartz wall gradually wears away on the inside until eventualbreak-through causes the lamp to fail.

The new flashing lamp has been standardized as with a rating of about 50Watt seconds per flash when operated at 40 flashes per minute. The poweris supplied from a 2000 volt charge on a 25 microfarad condenser. Therate of energy consumption during the flash is obtained by dividing theenergy per flash by the flash duration and is found to be 3,000,000Watts. obtained by dividing the output in a direction perpendicular tothe lamp axis by the size of the light source viewed from the samedirection, and is found to be 10,000,000 candlepower per square inch.

The flash current is calculated using the formula for the discharge ofcondenser T=RC. Since C is made 25 microfarads and T is measured to be17 microseconds, R is found to be .68 ohm.

With 2000 volts applied to .68 ohm, the peak current estimated by Ohmslaw is 2940 amperes. The average power used in the lamp is obtained bydividing the energy per flash by the interval between flashes and isfound to be only 33 watts.

Krypton gas is used in the lamp to obtain the maximum light efficiency.Argon gas will give about 80% as much light and nitrogen still less.

Referring to the drawing in detail, like parts being designated by likereference characters, there is shown in Figure 1 a lamp embodying ourinvention and comprising :an envelope I I with an intermediate tubularportion I2, preferably formed of tough transparent vitreous materialsuch as fused quartz, fused magnesia, fused alumina, or similarrefractory material. In a preferred embodiment, the intermediate portionI2 is about 2" long, has an inside diameter of about 4 millimeters or1/5", and a wall thickness of about 3 millimeters. The envelope II holdsa pair of electrodes I3 and I4 desirably formed of tungsten, molybdenumor similar refractory or -high melting point metal. In a preferred form,they consist of relatively heavy solid or non-tubular, as distinguishedfrom hollow, tungsten cylinders, that is such about 1/8 in diameter thatis, nearly as large as the bore of the portion I2, and about 1% long,presenting to one another flat faces relatively large in area. Theseelectrodes are disposed in end chambers I5 and I6, respectivelyextending from opposite ends of the quartz tubular portion I2. The endchambers are formed as graded seals, desirably hermetically sealed tothe quartz tube after first beading the ends of the latter with rings ofspecial flux glass I1, using a glass lathe.

The graded seal portions forming the end chambers I5 and I6 may besealed directly to the electrodes I3 and I4, respectively. Preferably,each electrode has its outer end portion fitting in an end cup or cap I8or I9, and the caps are in The brightness is turn sealed to therespective ends of the graded seal portions I5 and I6. The cups I8 andI9 are desirably formed of material which seals well to the glass of theend chamber members I5 and I6. For that purpose, they may be formed ofKovar as defined in the Lempert et al. Patent No. 2,279,831, dated April14, 1942, or other suitable metal. Such cups are desirably degreased,baked in humid hydrogen, the tungsten electrodes chamfered at theirouter ends, then degreased and spot welded to the Kovar cups. Rings ofbrazing wire are then formed, degreased, and two rings applied over eachelectrode. A boat is used to hold each electrode assembly in a verticalposition with the Kovar cup down. Heating in a humid hydrogen atmosphereat about 1010 C. for about 20 minutes serves to braze each electrode toits cup, thereby making a good electrical connection therebetween.

Before securing the cup to the corresponding end chamber member, itsedge is desirably rst glassed, as on a lathe, oxidation removed as in ahot anodic alkaline electrocleaner, the parts rinsed in clean water,neutralized, again rinsed, and then dried.

An `assembled electrode and cup is secured to its graded seal and thelatter to the quartz tube, preferably in the following manner. A gradedseal with a protective ring of asbestos ribbon around its end is held ina lathe head chuck and la quartz tube with one end plugged with asbestosis held in the tail chuck. The adjacent ends of the parts are sealed,care being taken to avoid sealing to an unfluxed part of the quartztube.

The tail chuck is disengaged and the yasbestos plug removed from thequartz tube. The second graded seal, with one end corked and with aprotective ring of asbestos ribbon around the end, is placed in the tailchuck and a second seal made as before.

The tail chuck is disengaged and the cork removed from the graded seal.An electrode assembly is placed in the tail chuck and sealed to a gradedseal, care being taken that the electrode is not oxidized. A hole may beblown for the exhaust tubulation and an exhaust tube sealed thereabout.The tail chuck is disengaged and the exhaust tube may be bent around soit can be engaged in the tail chuck, care being taken that the exhausttubulation is disposed axially of the assembled lamp part. The gradedseal is desirably annealed while the exhaust tube is being held by thetail chuck.

The assembly is removed, turned around and put into the head chuck,where it is held by the exhaust tubulation, and an electrode assembly isplaced in the tail chuck, sealed to the graded seal and annealed,completing the assembly.

The complete assembly is then desirably connected to a vacuum pump andtested for leaks with a spark coil. rlhe lamp is then exhausted, baked,and then filled with an inert gas such as argon or nitrogen at apressure of about millimeters and tested by flashing two minutes atthree flashes per second, using a 24 microfarad condenser charged toabout 2000 volts. The polarity is reversed and this is repeated.Triggering is accomplished with the spark coil applied to the center ofthe quartz tubing. The lamp is then reevacuated and lled with kryptongas to a pressure of about 325 millimeters. The lamp is then preferablyflashed for about two minutes at about 40 flashes per minutes on 24microfarad condenser with a potential of 2000 volts. The

lamp .is then .tippedoff carebeing staken; taavoidl strainin the gradedsealsi In order. to `avoid inconsistent firing-duringuse,` bit-.gettingmore complete gasf.ionization,V weide. sirably. employ a trigger-2|,desirably formed of. suitable wire such as 1'5A `mil-spring1 steel.lorf/nickel"y and wound several times .-a-roun:l:the-quai-tz.-ti-xbe. I2,as illustrated, an intermediate portion there-i of, between end portionswhichfencirclethetube, being connected to the timing, mechanism indie..cated at 22a; For flashing, the-lampi'siconnectedt through aresistance2-3'1 to a.source-.ofdirect current 24, in parallelwitha-condenser-2'5`- The new lamp above .described avoids: the-use; ofan outer bulb andl vaporizediquartzcollected; in a way to obscure thelight. output.- Natural:f cooling of the lamp isthusA not impeded.Allin-Vm largedI or relatively largeend chambers L and- Is.4 serve tocollectv the.` vaporizedouartz, sinceithee rapid expansion ofgasduringaflash blowsiwhat.-m everis. vaporizedintofthernf. Thisl has. beenfound to .worlcoutioluite-y well lin practice, evenwith'loade. ingshigher-than 20; wattsaverage... Nostarting. electrode sealis. needed',sinceit hasbeenfound. that a wire, such as' indicated at. 2|-, wrappedVaroundthe quartz tube.-portion I21at the.4 center. of the lamp servesas.well.'` Thenewelamplends.v itself toy forced coolingfor higherload-ings:.b:et.` ter than anyV previously employed.- 'Ihe-.employ..ment7 of Kovar` cups, such -as .indicated at I Brand I9;A ratherv thanglassfares connected.directly-to the` tungsten'electrodes, hasavoided'considerable.;y shrinkage sdue to cracking, of fthe. glass'.dares-.

The lamp of ourinvention was rst testedfat20 to..30 watt secondsperflashfrom` 40 to 8041er4 minute. After 10 to. .20: hoursthevarious.lamps.r testedalldeveloped somev blackening obscuringf.y the. lightAoutput and voltagel .breakdown became. high sol that triggeringwaslinconsistent.. We.. thereforestepped up the. power. per -flaslbto-3.81 wattseconds and later to` 5.0fandreven as .highvasr 325. Contrary.to. expectations, the. operation .aty higherloading gavelexcellent'results. Blackening. Wasnot only` avoided, butblachened'-larxxpsivvould. become. clean. by raising.- the powerperflashz. Then.: voltage .break-down became moreconsistent,and.-4 lampswhich had becomehard to startwere made tol start wellagainby4 operating;fori as whileat higher power per ash'.

Examination of. dissected; g lamps; showed that; silica powdervcollected in .a-,hardfthick layer;` on the electrodesl When.l run at:low pQWel? .per :flashs the electrodes `coated over completelyfand the;starting voltage became-highka, Whenfrungat/h f, power per flash, thetip off-the,electrogigawouldL` y 55 cleaned, oir or lkept clean,while.powder,stillr e=. Inained onv the .electrode backgof thetip,where.v it did no` harm. Examination oi the. quartz. inter mediatetubeshowedl thatl the inside diameter was increasing with lamp operationdue tothe evaporation ofthe quartz atthe high loadings. v ItisA obviousthat any incipient black deposit`v is removed-by the evaporation of`lthequartz which is blown into the ends of a lamp around theeleetrodes.

Figure 2` shows the characteristics .of` the, lamp)-h of ourV invention4with; changesV in thee.capacity, of the condenser 25.- Witlracondenser/ofv 121 microfarad capacity; it will be ,seenY thatvlpeakgin-e.. tensity of the flash is only; aboutY 3 1 millions lumensas indicated by the graphe-26,;y When-Itho.. condenser capacityisdoubled, the peak lumens increased-to kmillion,asindicated by the graph2'I. When tripled, it increases to '74 million, as indicated bythegraph. 28. Whenlthe condenser 75 is.-.increased=to 60' microfarads,the-peaky intensity; is 100.8 million lumens, as indicated by the graphFigure 3i shows. othencharacteristicsof the lamp ,of-.ourfinventi'onIn-terms of vvattiseconds` per'. ash, the-lumens. per watt increaseAalong the curve 31|, the-.peak lumensincrease along the curve` 32;. theduration ofthe flashabove.- 1/3 peak in-Y creasesralong'the: curve 33,whilefthe lumen see-- i ondsioutputz varies .in accordance withv the.curven curve 31f'of a standard photographic ash lamp,

having; anfinput of -48 watt-seconds. Bystandardvphotographic flashlamp, we mean one of theftype designated IPT-14 by Harold Edgertonyin'his: article entitled Photographic use of Elec--v trical DischargeFla-shtubes, Abeg-inning on page 3,90" of ;volume 36, No. 7,. Journal ofthe. Optical- Societyfof America,.July, 1946; anddescribed by E.-Carlson and D. A.v Pritchard in their article entitled TheCharacteristics and Application of FlashtubesIl presented at the; AnnualConvention of fthe Illuminating Engineering.. Society, Quebec, Canada,September 18 to20, 1946.

Theash tube of'l this invention has: a shorter duration and.y higherTpeak output than other known photographic-flash lamps,v as graphicallydisclosed rFigure5becauseashort arc gap witharelatively highl gaspressure is provided thaty will `have lower resistance-` to the flashcurrent thana long.- straight or coiled discharge. tube; in whichthefgask pressure is quite low. The. same.` quantity of energy` is,usedup faster in thefl'amp offzthis invention. As a result, the hashdoes not. last as long andthe intensityof thelight, beingI proportionalto'thevrate of much higher.

Although preferred embodiments of .our invention. have been disclosed,it will; beunderstood thatmodications may be made withinV the spirit:

and scopeof. the appended claims.. For-example, although krypton gas is.specied as preferred, yetgas containing a `rrnajor proportionofrkrypton, say saft'y 10% gives, an output approximating that whenpurekrypton iskused.. Other rare or noble gases, such as argon, xenon,neon, helium, or` mixtures,`may be employed if4 the corresponding,

variations in Ioutput are permissible. The effect,

of pressure, of krypton, forexample, yon. light efflciency was foundl tobe relatively unimportant, soA that the most advantageous pressure forthe desired-breakdown characteristics may be used.`

Although we do-not wish to limit ourselves tothe size of the bore of theintermediate tubular portion I2,l yetV we may -desire todecrease itformakeit soy small that the discharge therethrough is saturated, that is,lls the entire cross-sectionv of the. .bore andi cannot be` furtherincreased at thevpressurezused lby increasing the .size of thecondenserf- Use at saturationcurren-ts notpnlymeans that the spectralcharacteristics of the energy consumption; is

and. aminorproportion of xenon, K

flashes are uniform, but that blackening is avoided.

We claim:

1. The method of making a discharge device comprising forming endchamber portions as graded seals, forming a pair of solid cylindricalmetal electrodes, chamfering an end of each electrode for fitting in anend cup, fitting the chamfered end of each electrode into a cup of Kovarand spot welding it thereto, placing rings of brazing wire over eachelectrode, heating each electrode and associated cup in humid hydrogenat a temperature of about 1010 C. for about 20 minutes to braze eachelectrode toits cup, glassing the free edge of the cup of each electrodeassembly, holding one of said graded seals with a protective ring ofasbestos ribbon around its end in a lathe head chuck and a quartzintermediate portion tube with one end plugged with asbestos in the tailchuck of said lathe, sealing the adjacent ends of the parts, using aspecial flux glass on the quartz tube, disengaging the tail chuck andremoving the asbestos plug from the quartz tube, plugging a secondgraded seal and holding it with a protective ring of asbestos ribbon inthe tail chuck, making a second seal between it and the other end ofsaid quartz tube, placing an electrode assembly in the tail chuck andsealing it to a graded seal, care being taken to avoid oxidation of theelectrode, removing the assembly, turning it around and holding it inthe head chuck, placing the other electrode assembly in the tail chuck,and sealing it to the other graded seal.

2. A discharge lamp comprising an intermediate fused quartz tubularportion, thick-walled to insure long life metal cup terminals one ateach end thereof, graded seal glass portions forming end chambers withsaid metal cup terminals and hermetically sealing the respective ends ofsaid low thermal expansion quartz portion to the higher thermalexpansion metal terminals to complete the envelope of said lamp, a solidor non-tubular cylindrical refractory metal electrode, nearly as largein diameter as the bore of the tubular portion, extending inwardly fromeach metal terminal, disposed in the adjacent chamber, presenting to oneanother dat faces relatively large in area, and aligned axially withsaid envelope, each metal terminal having an inwardly opening socket, inwhich the outer end portion of its electrode is received and brazed, anda ange portion surrounding and spaced from its electrode, the free edgeportion of said flange being hermetically sealed to the adjacent edgeportion of said graded seal portion, and a filling of rare gas in saidenvelope.

3. A gas-filled discharge lamp comprising a thick-walled quartz tubeabout 2" long and l/5 inside diameter, a graded seal glass chamber oflarger diameter hermetcally sealed to each end of and communicating withsaid tube, and solid refractory metal electrodes, nearly as large indiameter as the bore of said tube, presenting to one another fiat facesrelatively large in area, disposed axially of said tube, one in eachchamber.

4. A discharge lamp comprising an envelope, said envelope having anintermediate fused quartz tubular portion, thick-walled to insure longlife, and metal cup terminals at each end thereof, said metal cupterminals closing the envelope and being hermetically sealed to therespective ends of said tube by graded seal portions forming endchambers and completing the envelope, a solid or non-tubular cylindricalrefractory metal electrode, nearly as large in diameter as the bore ofsaid tubular portion, extending inwardly from each metal terminal,disposed in the adjacent chamber, and aligned axially with saidenvelope, and a rare gas filling in said envelope.

5. A gas-filled discharge lamp comprising an outer tube of translucentrefractory material selected from the group consisting of fused quartz,fused magnesia, and fused alumina, a glass chamber hermetically sealedto each end thereof, metal cup terminals at the outer ends of said glasschambers, and a solid or non-tubular metal electrode, nearly as large indiameter as the bore of said tube, in each chamber, presenting a flatsurface to the other electrode with its outer end secured to the innersurface of the corresponding terminal, and disposed axially of saidtube.

6. A discharge lamp comprising an intermediate tube of translucentrefractory material selected from the group consisting of fused quartz,fused magnesia and fused alumina, about 2" long, 1/5 inside diameter and3 mm. wall thickness, metal cup terminals one at each end of said lamp,graded seal glass portions, of a diameter larger than said refractoryportions. forming end chambers with said metal cup terminals andhermetically sealing the respective ends of said refractory portionsthereto to complete the envelope of said lamp, a solid or nontubularcylindrical tungsten electrode about 1/8 in diameter and 1%" longextending inwardly from each metal terminal, disposed in the adjacentchamber, presenting a flat surface to the other electrode and alignedaxially with said envelope, each metal terminal having an inwardlyopening socket in which the outer end portion of its electrode isreceived and connected, and a flange portion surrounding and spaced fromits electrode, the free edge portion of said flange being embedded in,and hermetically sealed to, the outer edge portion of the adjacent glassend chamber, and a lling of noble gas comprising a major proportion ofkrypton at a pressure of about 325 millimeters in said envelope.

7. The method of making a discharge device comprising forming endchamber portions as graded seals, forming a pair of solid cylindricalrefractory metal electrodes, tting an end of each electrode into a metalcup and electrically connecting it thereto to make the electrodeassemblies, glassing the free edge of the cup of each electrodeassembly, holding one of said graded seals with a protective ring aroundits end in a lathe head chuck and a quartz intermediate portion tubewith one end plugged in the tail chuck of said lathe, sealing theadjacent ends of the parts, disengaging the tail chuck and unpluggingthe quartz tube, plugging a second end chamber portion and holding itwith a protective ring in the tail chuck, making a second seal betweenit and the other end of said quartz tube, placing an electrode assemblyin the tail chuck and sealing it to a graded seal, removing theassembly, turning it around and holding it in the head chuck, placingthe other electrode assembly in the tail chuck, and sealing it to theother graded seal.

GEORGE A. FREEMAN. CARL G. ANDERSON, JR.

(References on following page) Number Name Date Meyer Sept. 20, 1932Howe Oct. '11. 1932 Davies Nov. 21, 1933 Wiegand Aug. 28, 1934 ZecherOct. 6, 1936 Gooskens May 3, 1938 10 Cox Dec. 27, 1938 Meyer Dec. 5,'1939 Number 10 Name Date Zecher Sept. 3, 1940 Suits May 13, 1941Rentschler Sept. 2, 1941 Aicher Dec. 23, 1941 Beese Sept. 15, 1942 GrierFeb. 15, 1944 Marden Jan. 16, 1945 Blackburn Sept. 25, 1945 GermeshausenApr. 30, 1946 Herzog Dec. 23, 1947

